Research On The Adsorption Of S/H And The Corrosion Resistance Of High-nitrogen Steel

The corrosion problem in oil gas field is extremely serious nowdays. The conventional steels used in oil gas field cannot meet the requirements of severe corrosive environment either for the service life or for the high cost. High nitrogen steel（HNS） exhibits excellent resistance to local corrosion and stress corrosion, also shows enhanced mechanical properties, which can be widely used in oil gas field in future.In this paper, the influence of nitrogen in γ-Fe on the adsorption and adsorption energy of Sulphur/hydrogen atom were studied by first principles calculations. The electrochemical corrosion properties of HNS in corrosion environment containing Na2 S and CO₂ and environment containing various ions were tested by electrochemical methods. The passivation stability and corrosion rules of HNS in oil field environment were analyzed. The pitting sensibility of HNS in Cl- and HCO3- mixed solution was obtained. The research can provide the experimental basis for the application of HNS in oil gas field.The results of first principles calculations showed that the adsorption energy of Sulphur atom on the surface of γ-Fe increasing and the distribution of the DOS of γ-Fe（100） moving to high energy area, which showed, the stability of the adsorption structure decreasing. The stable adsorption position of Hydrogen atom changed from bridge position to hole position when adding nitrogen to γ-Fe. The adsorption energy of hydrogen atom decreased, and the stability of the adsorption structure of hydrogen atom on the surface of γ-Fe increased.The results of the electrochemical tests of HNS in corrosion environment containing Na2 S and CO₂ showed that the corrosion resistance of HNS enhanced. In the same corrosion environment, the passive current density of HNS was 7.192×10-4A·cm-2, the initiating passive potential was-0.2047 V and the passive film resistance was 69853 Ω·cm2. The corrosion resistance of 316 L came second and Cr13 steel is the worst. With the increasing of concentration of Na2 S, the pitting potential of HNS decreased and the passive current density increased. The passive film resistance was also decreased, and the passivation stability of HNS decreased. With the increasing of the temperature, the corrosion potential of HNS decreased, so did the pitting potential. The charge transfer resistance decreased, as well as the passive film resistance. The passivation stability of HNS decreased with the increasing of the temperature.The pitting corrosion behavior of HNS is affected by the synergistic reaction of Cl- and HCO3- in mixed solution. The increasing of Cl- can increase the pitting sensitivity of HNS. The change of Cl- have little influence on the pitting sensitivity of HNS when the concentration of HCO3- reached high value. When the concentration of Cl- was less than 0.025mol/L, the increasing of HCO3- can increase the pitting sensitivity of HNS. When the concentration of Clwas higher than 0.25mol/L, the increasing of HCO3- can reduce the pitting sensitivity of HNS.